Ruby-on-rails 搭建脚手架时建立关系
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Create relationships when scaffolding
提问by Stefan Bossbaly
Hi I am new to Ruby on Rails. I am trying to create a small blog site. I have two tables Posts and Comments. Each Post will have many comments. I generate the tables using these commands.
嗨，我是 Ruby on Rails 的新手。我正在尝试创建一个小型博客站点。我有两个表 Posts 和 Comments。每个帖子都会有很多评论。我使用这些命令生成表。
rails g scaffold Post title:string body:text author:string
rails g scaffold Comment body:string author:string
Now I want to add the relationship to the model classes. I add has_many :commentsto the Post class and belongs_to :postto the Comment class. However when I try to call post.commentsI get a runtime error saying SQLException: no such column: comments.post_id. Should I create a migration and add post_id under Comment or is there a way to achieve this when scaffolding?
现在我想将关系添加到模型类。我添加has_many :comments到 Post 类和belongs_to :postComment 类。但是，当我尝试调用时，post.comments我收到一个运行时错误，说SQLException: no such column: comments.post_id. 我应该创建一个迁移并在 Comment 下添加 post_id 还是在搭建脚手架时有办法实现这一点？
回答by JamieD
Scaffold actually provides a way to generate relationships, you should use the :referencesdata type
Scaffold 实际上提供了一种生成关系的方式，你应该使用:references数据类型
rails g scaffold Comment body:string author:string post:references
This will generate a migration for the comments table with a post_id field and index for it. The generator will also add belongs_to :postto the Comment model.
这将为带有 post_id 字段和索引的 comments 表生成迁移。生成器还将添加belongs_to :post到 Comment 模型中。
It will not however generate the reverse side of the relationship so you'll need to add
但是，它不会生成关系的反面，因此您需要添加
has_many :comments
to the Post model yourself. You will also need to add nested resource routing if this is something you need as the generator can not handle this.
到 Post 模型自己。如果这是您需要的，您还需要添加嵌套资源路由，因为生成器无法处理此问题。
回答by agmin
You are definitely on the right track. If you add the post_idcolumn when generating the Commentscaffold your relationship will then work (although you still need to add the has_many :commentsand belongs_to :post)
你绝对是在正确的轨道上。如果post_id在生成Comment脚手架时添加列，则您的关系将起作用（尽管您仍然需要添加has_many :comments和belongs_to :post）
So the updated generator call would look like this:
所以更新后的生成器调用看起来像这样：
rails g scaffold Comment body:string author:string post_id:integer
回答by Jeremy Lynch
You can also use belongs_tolike this:
你也可以belongs_to这样使用：
rails g scaffold Comment body:string author:string post:belongs_to
